The present invention relates to a piston machine in general, and more particularly to a radial piston machine, such as a pump or motor.
Radial piston machines of the foregoing type have been known and have been disclosed, for example, in applicant's U.S. Pat. Nos. 3,985,065 and 3,893,376.
Mass flows of the pressure medium which pass through controlled profiles of such known so-called spool valve-controlled piston machines, particularly pumps, with a usual configuration of the pintle, occur in the dead centers within very short periods of time firstly against the direction of feeding (pressure-compensation-stream due to compressibility of the pressure medium) and then in the feeding direction. High pressure differences during the pressure-compensating steps cause in the control grooves the stream speeds which can be in the range of many hundred meters per second. The mass of the flowing pressure medium is, however, small despite the fact that the movement energy for quick steps to change directions cannot be neglected. This energy causes a delayed adjustment of the stream speeds to the changes in the directions of pressure medium flows. This leads to the disadvantage that upon the change from the high-pressure side to the low-pressure side in the inner dead center of the pump the pressure medium flows from the cylinder block to the low-pressure side of the pump only over a short time, also when the cylinder block pressure has already fallen below the level of low pressure. During the reverse from the low-pressure side to the high-pressure side in the outer dead center of the pump, the pressure medium flows for a short time from the high-pressure line into the cylinder block also when the cylinder block pressure has already risen above the level of the high pressure. This leads to distortion of the pressure medium course and impairing of the filling of the cylinder. Both these drawbacks increase noise emission and feeding stream pulsation of the pump.